gh-112075: Accessing a single element should optimistically avoid locking #115109
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DinoV
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Objects/dictobject.c
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| set_keys(mp, new_keys_object(interp, log2_newsize, unicode)); | ||
| if (mp->ma_keys == NULL) { | ||
| mp->ma_keys = oldkeys; | ||
| set_keys(mp, oldkeys); |
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I don't think the possible temporary assignment to NULL is thread-safe without the GIL. Let's assign the result of new_keys_object() to a temporary variable and check that before assigning it to mp->ma_keys.
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When I was looking at this function when you made a comment about it on #114741 I realized that the assignment of it to a new empty table isn't right at all! We really need to allocate the new table, copy everything over, and then we can publish it.
Objects/dictobject.c
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| @@ -3591,11 +3942,18 @@ dict___contains___impl(PyDictObject *self, PyObject *key) | |||
| if (hash == -1) | |||
| return NULL; | |||
| } | |||
| #ifdef Py_GIL_DISABLED | |||
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Does this differ from PyDict_Contains()? Can we just call that?
| @@ -4157,10 +4534,20 @@ _PyDict_Contains_KnownHash(PyObject *op, PyObject *key, Py_hash_t hash) | |||
| PyObject *value; | |||
| Py_ssize_t ix; | |||
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| #ifdef Py_GIL_DISABLED | |||
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This also looks like contains_known_hash
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Or does contains_known_hash look like this? 🤔
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…id locking (python#115109) Makes accessing a single element thread safe and typically lock free
…id locking (python#115109) Makes accessing a single element thread safe and typically lock free
…id locking (python#115109) Makes accessing a single element thread safe and typically lock free
Makes accessing a single element thread safe.
Adds tracking for whether a dictionary is shared or not, but some of this gets duplicated in #115108.
Does not yet deal with all of the atomic assignments that need to happen to make this 100% right, that'll come in a separate PR.
dictobjects thread-safe in--disable-gilbuilds #112075